In a process for manufacturing a LCD or the like, various plasma processing apparatuses such as a plasma etching apparatus, a plasma CVD film forming apparatus and the like are used to perform a predetermined process on a glass substrate. Conventionally, a capacitively coupled plasma processing apparatus has been widely used as the plasma processing apparatus. Recently, however, attention has been paid to an inductively coupled plasma (ICP) processing apparatus capable of generating a high-density plasma.
A high frequency antenna is provided at an outer side of a dielectric window of a processing chamber for accommodating a target substrate to be processed. In the processing chamber, an inductively coupled plasma is generated by supplying a processing gas to the processing chamber and applying a high frequency power to the high frequency antenna. By using the inductively coupled plasma thus generated, a predetermined plasma processing is performed on the target substrate. A planar antenna having a predetermined pattern is widely used for the high frequency antenna of the inductively coupled plasma processing apparatus (see, e.g., Japanese Patent Publication No. 3077009).
Recently, a target substrate to be processed has been increased in size. For example, a rectangular glass substrate for use in an LCD is considerably scaled up from about 1500 mm×1800 mm (short side×long side) to about 2200 mm×2400 mm and further to about 2800 mm×3000 mm.
In the inductively coupled plasma processing apparatus, a dielectric window is interposed between the high frequency antenna and a plasma generation region in the processing chamber. As the substrate to be processed is scaled up, the dielectric window is scaled up. As described in Japanese Patent Publication No. 3077009, the dielectric window is generally made of quartz glass or ceramic.
However, quartz glass or ceramic is soft and thus is not suitable for the scaling up of the dielectric window. Japanese Patent Publication No. 3609985 discloses a measure to divide quartz glass to deal with the scaled up dielectric window.
Since, however, the target substrate to be processed is scaled up considerably, it is difficult to deal with the scaled up dielectric window by the measure disclosed in Japanese Patent Publication No. 3609985.
Hence, Japanese Patent Application Publication No. 2011-29584 discloses a technique capable of dealing with the scaling up of the target substrate to be processed by substituting a dielectric window with a metal window having an increased strength.
The technique described in Japanese Patent Application Publication No. 2011-29584 can deal with the scaling up of the substrate to be processed. Since, however, a plasma generation mechanism in a metal window is different from that in a dielectric window, there occurs a separate problem related to the scaling up of the metal window. For example, an eddy current circulating in a loop through the metal window is diffused in a direction perpendicular to a current flow direction (hereinafter, simply referred to as “diffusion of eddy current”), and it is difficult to control plasma distribution in the processing chamber.